This invention relates to a thrust ball bearing in which is mounted a retainer formed by pressing a metal plate.
In an ordinary thrust ball bearing, a plurality of balls, mounted between two bearing rings, are rollably retained by an annularly formed retainer (see e.g. “Rolling Bearing Handbook edited by J. Brändlein et al, translated by Takeo Yoshitake, published by Kogyo Chosa-kai in 1996”, pages 32–33).
FIG. 3 shows an example of such a thrust ball bearing. This bearing comprises an outer ring 51, an inner ring 52, a plurality of balls 53 mounted between these bearing rings 51 and 52, and a retainer 54 rollably retaining the balls 53. The retainer 54 is annularly formed by pressing a metal plate, and has pockets 55 for receiving the respective balls 53, formed at predetermined intervals in the circumferential direction. Its inner portion 56 and outer portion 57, which embrace the balls 53 received in the pockets 55, are formed by bending. These side portions 56 and 57 of the retainer 54 are drawn so that the distance between the side portions at portions between the adjacent pockets 55 is narrow to keep the balls 53 from falling.
In this thrust ball bearing, as shown in FIGS. 4 and 5, when the balls 53 turn about a common axis while pushing and advancing the retainer 54 as the inner ring 52 rotates, the respective balls 53 and the retainer 54 are in slide contact with each other at one point only, i.e. at the corner portion of the peripheral edge of each pocket 55.
Thus, at the slide contact position of the balls 53 and the retainer 54, the contact surface pressure increases, so that lubricating oil stuck on the surfaces of the balls 53 tends to be scraped off, and thus wear of the retainer 54 tends to progress. Further, if the amount of wear of the retainer 54 or the balls 53 increases, wear powder trapped between the raceways of the bearing rings 51 and 52 and the balls 53 may cause premature breakage of the bearing ring 51 or 52 or the balls 53.
In particular, as with bearings mounted in HSTs (hydrostatic transmissions), in case they are used under conditions where uneven loads act, the speeds at which the respective balls rotate about a common axis tend to vary, so that the contact surface pressure between part of the balls and the retainer at slide contact positions tends to further increase. Thus, the possibility of the above problem occurring is high.
An object of this invention is to reduce the contact surface pressure between the balls and the retainer of the thrust ball bearing at slide contact positions, thereby suppressing the wear of the retainer.